In view of environmental problems, development of power supply apparatuses that uses sunlight, wind power, wave power, tidal power, tidal energy, and other natural energy is being pursued in recent years. However, power generation methods that use natural energy have the drawback that the energy density is low. Another drawback is that the output of electric power generated in these methods is affected by weather conditions and is thereby varied, preventing electric power from being stably supplied at all times.
In Patent Literature 1, for example, to prevent an overcurrent in a wind power generator from flowing into a secondary battery, a wind power generation apparatus is proposed that detects the voltage of a smoothing capacitor in the wind power generator; the wind power generation apparatus interconnects the secondary battery and wind power generator when the voltage of the smoothing capacitor becomes substantially the same as the voltage of the secondary battery, and interconnects the wind power generator and secondary battery through a current-limiting circuit when there is a difference in these voltages.
In Patent Literature 2, a charging control apparatus is indicated in which a charging control unit identifies the battery cell having the lowest cell voltage from a plurality of battery cells connected in series in a battery according to detection results of cell voltages detected by a cell voltage detecting unit, after which the charging control unit individually turns on and off a plurality of switches, each of which is connected between each two of the plurality of battery cells and stores electric power obtained by photovoltaic batteries in the identified battery cell, enabling the remaining capacities in all battery cells to be efficiently equalized.
In Non-Patent Literature 1, a photovoltaic generation system is indicated in which a capacitor is connected in parallel to each of a plurality of photovoltaic battery modules; when any photovoltaic battery module is shadowed, it is temporarily disconnected from a photovoltaic battery module array by a metal-oxide-semiconductor field effect transistor (MOSFET), and after other capacitors have been adequately charged, the disconnected photovoltaic battery module is connected to the array again.